[PATCH] arm: kirkwood: Enable uart0 dm-pre-reloc for Kirkwood boards

[Tony Dinh]

Hi Stefan,

On Thu, Feb 2, 2023 at 8:28 PM Tony Dinh <mibodhi at gmail.com> wrote:
>
> Hi all,
>
> On Thu, Feb 2, 2023 at 3:59 PM Tony Dinh <mibodhi at gmail.com> wrote:
> >
> > Hi all,
> >
> > On Thu, Feb 2, 2023 at 10:04 AM Pali Rohár <pali at kernel.org> wrote:
> > >
> > > On Wednesday 01 February 2023 13:13:16 Tony Dinh wrote:
> > > > Hi all,
> > > >
> > > > On Wed, Feb 1, 2023 at 11:05 AM Pali Rohár <pali at kernel.org> wrote:
> > > > >
> > > > > On Wednesday 01 February 2023 09:17:15 Michael Walle wrote:
> > > > > > > > > When DM_SERIAL is enabled, the device-tree property dm-pre-reloc is
> > > > > > > > > required to boot over UART with kwboot. Enable this in a Kirkwood
> > > > > > > > > common u-boot dtsi.
> > > > > > > >
> > > > > > > > My (dev) board unfortunately, have a bootloader which can't boot over
> > > > > > > > serial.
> > > > > > >
> > > > > > > This is feature of Marvell BootROM and does not require any special from
> > > > > > > Bootloader. So you should be able to boot over UART (if you have
> > > > > > > accessible pins).
> > > > > >
> > > > > > I know, but there are known versions ob the bootrom where uart boot
> > > > > > isn't supported (correctly).
> > > > >
> > > > > I heard about it... maybe it is a bug in client software (kwboot)? I do
> > > > > not have such board if you are interested in it I could try to send some
> > > > > details how to debug it.
> > > >
> > > > The Kirkwood SoCs came with different BootROM versions. Version 1.1
> > > > cannot be booted over UART, but version 1.2  can. I think there must
> > > > be a bug in the BootROM 1.1. The older Kirkwood such as Sheevaplug,
> > > > Dockstar, iConnect boards come with BootROM 1.1. Later version of
> > > > Sheevaplug, GoFlex Home, GoFlex Net, Dreamplug, Pogoplug V4, Zyxel
> > > > NSA310S, NSA320, NSA325 come with BootROM 1.2. So even though it is
> > > > the same SoC, eg. 6281, they are actually produced at a different time
> > > > and have different BootROM versions.
> > >
> > > There are always multiple revisions of the same SoC. So it is possible
> > > that something was broken on first revision of 88F6281 and in next
> > > revision was updated BootROM with some fixes. Revision is written on
> > > package label and for Armada SoCs it is available also in some register
> > > (not sure about Kirkwood). It looks like that there is at least revision
> > > Z0 and revision A0 of some Kirkwood SoC.
> > >
> > > If there is a bug in first revisions then it should be documented in
> > > some Kirkwood Errata document. Unfortunately I have never seen it, it is
> > > not public, so I have no idea. In any case, if somebody has access to
> > > Marvell documents, interesting are these document numbers:
> > >
> > > * MV-S105223-001 - Differences Between the 88F6192, and 88F6281 Stepping Z0 and A0
> > > * MV-S501081-00 - 88F6180, 88F6192, and 88F6281 Functional Errata, Interface Guidelines, and Restrictions
> > > * MV-S501157-U0 - 88F6180, 88F6190, 88F6192, and 88F6281 Functional Errata, Interface Guidelines, and Restrictions
> > >
> > > One of the option how to investigate or debug this issue without
> > > documentation is to dump both BootROM versions (1.1, 1.2) and compare
> > > them. Either there is different UART protocol for booting (which needs
> > > to be implemented) or UART protocol is buggy and needs some workaround
> > > or it is completely broken and does not work.
> >
> > Here is an excerpt from doc/develop/driver-model/serial-howto.rst.
> >
> > Quote ===
> > Here are some things you might need to consider:
> >
> > 1. The serial driver itself needs to be present before relocation, so that the
> >    U-Boot banner appears. Make sure it has a u-boot,dm-pre-reloc tag
> > in the device
> >    tree, so that the serial driver is bound when U-Boot starts.
> >
> >    For example, on iMX8::
> >
> >        lpuart3: serial at 5a090000 {
> >            compatible = "fsl,imx8qm-lpuart";
> >            ...
> >        };
> >
> >    put this in your xxx-u-boot.dtsi file::
> >
> >        &lpuart3 {
> >            u-boot,dm-pre-proper;
> >        };
> > === Unquote
> >
> > So it looks like my understanding was correct. The serial driver is
> > not bound if there is no u-boot,dm-pre-reloc tag. And does it sound
> > like it is required for all targets because of this reason?
>
> Well, after giving it some thought I think my reasoning is not sound.
> There must be a bug somewhere that the Pogo V4 triggers (the board
> that has a silent console, and then freezes, when dm-pre-reloc is not
> used for uart0).
>
> Because, even if the serial driver is not bound to the uclass, it
> should boot with the silent console regardless? and after relocation,
> u-boot should bind the serial driver, and we'd just lose the banner
> part?
>

I'm withdrawing this patch :)

I've run the kwboot test on another Kirkwood board (NSA310S) without
the u-boot,dm-pre-reloc tag, and it booted flawlessly! In fact, I
could not cause it to hang like the Pogo V4. U-boot banner and
everything was output as it normally would be. So the unsolved problem
is specific to the Pogo V4, and the u-boot,dm-pre-reloc tag just
happened to fix it. I'll run with DEBUG_UART to see if I can see a bit
more clearly.

The documentation for DM serial  in
doc/develop/driver-model/serial-howto.rst is probably somewhat
obsolete. At least it is not applicable to some Kirkwood boards.

All the best,
Tony